The ultrasonic fluid measurement apparatus is for letting fluid flow through measurement flow passages, letting an ultrasonic wave propagate through an interior of the measurement flow passage, measuring an ultrasonic wave propagation time, and determining a fluid flow rate from resultant measurement information.
The measurement flow passage assumes a rectangular shape that is oblong in cross section. A pair of ultrasonic transceivers are provided in neighborhoods of respective mutually-opposing short sides of the flow passage.
The pair of ultrasonic transceivers are arranged in such a way that an ultrasonic wave propagation path is formed at a predetermined angle with respect to a flowing direction of the measurement flow passage; namely, that the ultrasonic wave propagation path obliquely crosses a flow of fluid.
An ultrasonic fluid measurement apparatus recently proposed for enhancing accuracy of measurement includes a plurality of diaphragms placed in parallel within a measurement flow passage, to thus implement the measurement flow passage as a multilayered flow passage.
FIG. 23 shows a related art multilayered flow passage member of this type, and a flow passage unit 101 is partitioned by straightening plates 102, to thus create a plurality of small flow passages 103.
The plurality of straightening plates 102 and a support 104 that supports the straightening plates 102 are integrally formed by use of a thermosetting resin.
Specifically, the support 104 is molded while the plurality of straightening plates 102 remain inserted.
Since the straightening plates 102 and the support 104 supporting the straightening plates are integrally formed, the molding operation obviates a necessity for operation of inserting the straightening plates 102 one by one into the support 104.
Since the straightening plates and the support are integrally formed by use of the thermosetting resin, contraction which will occur during hardening of the resin can be lessened when compared with a case where they are integrally formed by use of a thermoplastic resin.
As shown in FIG. 24, another example multilayered flow passage member appears to have a measurement duct member 111 in which each of grooves 112 is made up of an opening 113 and a housing portion 114.
The housing portion 114 is formed at a depthwise end of the groove 112, and a size of the opening 113 is set so as to become greater than a thickness of a straightening plate 115.
The straightening plate 115 is inserted into the groove 112 through the opening 113. Since a height of the housing portion 114 is equal to the thickness of the straightening plate 115, the housed straightening plate 115 comes into contact with an interior wall surface of the housing portion 114, to thus be supported by the interior wall surface.
An area of the groove 112 extending from the opening 113 to the housing portion 114 (hereinafter called a “guide area”) is formed in a shape such that a size of opening of the area becomes gradually smaller. Specifically, a slope 116 is formed in the guide area from the opening 113 to the housing portion 114.
Therefore, upon contact with the guide area during insertion, the straightening plate 115 is guided toward the depthwise end of the groove 112 along the slope 116.
The straightening plate 115 guided toward the depthwise end is housed into the housing portion 114 located at the depthwise end, as mentioned above.
Since the straightening plate 115 is guided into the housing portion 114 by the guide area, it is possible to continually perform insertion of the straightening plate 115 even when a tilt (or a misalignment) exists between the straightening plate 115 and the housing portion 114 within a range of the size of the opening 113 during inserting operation.
Thus, the degree of freedom of positional relationship between the straightening plate 115 and the housing portion 114 achieved during insertion is increased, which in turn facilitates fitting of the straightening plate 115.
Since the housing portion 114 supports, in a contacting fashion, the straightening plate 115 in a housed state, occurrence of a rattle in the straightening plate 115 can be prevented, or the rattle can be lessened (see; for instance, Patent Documents 1 through 3).